1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display device or an EL display device and more particularly to a technique for effectively decreasing the number of wirings from a video line drive circuit or a scanning line drive circuit to a display panel.
2. Background Art
At present, liquid crystal display panels used for liquid crystal televisions or mobile phones are TFT type liquid crystal display devices.
FIG. 1 shows an equivalent circuit of a conventional TFT type active matrix liquid crystal display panel.
As shown in FIG. 1, the conventional liquid crystal display panel includes a plurality of scanning lines (also referred to as gate lines) (GL) arranged in parallel in the y-direction and extending in the x-direction and m video lines (also referred to as source lines or drain lines) (DL) arranged in parallel in the x-direction and extending in the y-direction on the surface on the liquid crystal side of one of a pair of substrates which are arranged to face each other via liquid crystal.
Regions surrounded by the scanning lines and the video lines constitute sub-pixel regions. In one of the sub-pixel regions, a thin film transistor (TFT) constituting an active element in which a gate thereof is connected to the scanning line, a drain (or source) thereof is connected to the video line, and a source (or drain) thereof is connected to a pixel electrode (PX) is provided.
Since liquid crystal is present between the pixel electrode (PX) and a counter electrode (CT), a liquid crystal capacitor (Clc) is formed between the pixel electrode (PX) and the counter electrode (CT). A holding capacitor (Cadd) is actually formed between the pixel electrode (PX) and the counter electrode (also referred to as common electrode) (CT). In FIG. 1, however, the holding capacitor (Cadd) is not illustrated.
Each of the scanning lines (GL) is connected to a vertical scanning circuit (also referred to as gate driver) (XDV). The vertical scanning circuit (XDV) sequentially supplies a selection scanning signal to each of the scanning lines (GL). Each of the video lines (DL) is connected to a horizontal scanning circuit (also referred to as source driver or drain driver) (YDV). The horizontal scanning circuit (YDV) outputs a video voltage of R, G, or B (so-called gray scale voltage) to each of the video lines (DL) during 1 horizontal scanning period.
A thin film transistor (TFT) using an amorphous silicon layer for a semiconductor layer (hereinafter referred to as a-Si thin film transistor) and a thin film transistor (TFT) using a polysilicon layer for a semiconductor layer (hereinafter referred to as poly-Si thin film transistor) have been known. Further, in recent years, a thin film transistor (TFT) using a microcrystalline silicon layer for a semiconductor layer (hereinafter referred to as microcrystalline thin film transistor) has also been known. The microcrystalline thin film transistor offers performance about intermediate between the a-Si thin film transistor and the poly-Si thin film transistor.
In general, while liquid crystal display panels for liquid crystal televisions use the a-Si thin film transistors as active elements, liquid crystal display panels for mobile phones use the poly-Si thin film transistors as active elements.
The operation speed of the poly-Si thin film transistor is about one digit higher than that of the a-Si thin film transistor. Therefore, in the liquid crystal display panel using the poly-Si thin film transistor as an active element, the vertical scanning circuit (XDV) is configured with the poly-Si thin film transistor, and the vertical scanning circuit (XDV) is formed on the surface on the liquid crystal side of one of a pair of substrates which constitute the liquid crystal display panel.
Since the operation speed of the a-Si thin film transistor or the microcrystalline thin film transistor is lower than that of the poly-Si thin film transistor, the vertical scanning circuit (XDV) formed of the a-Si thin film transistor cannot be formed inside a liquid crystal display panel. Therefore, in the liquid crystal display panel using the a-Si thin film transistor or the microcrystalline thin film transistor as an active element, a semiconductor chip having the vertical scanning circuit (XDV) installed thereon is mounted on one of a pair of substrates which constitute the liquid crystal display panel, for example.
Examples of the related art document relating to the invention include JP-A-2001-305510.